Definition

Minerals can be defined as inorganic, chemical and physicallyhomogenous and usually solid materials of which the composition can be defined with a chemical formula. That sounds very complicated, but in reality this just means that every non-living natural thing which you can stick a label on with it's chemical formula is in fact a mineral.. do note though that a natural aggregate (joined parts that are mechanically seperable) is also a mineral

This means that contrary to popular belief that stones are indeed (a special category of) minerals. For the record.. The study of stones is called petrography.. (so is writing on stones but that's besides the point).

Like stones; Metals are also minerals provided they were formed by natural processes (Studying metals and their properties is called metallurgy)

Minerals may not contain synthetic material, or may be synthetically formed.. These compounds are not minerals.

Sometimes, one mineral can be formed by several different processes, though it's very hard to trace exactly how a single mineral was formed, important clues can be found in active vulcanoes, warm water springs and by studying layers of sediment in lakes and oceans.

More on the formation.. aka the boring part

Mineral forming processes can generally be split up into the following categories;

Magmatic mineralization: Magma normally contains high quantities of nearly every chemical element, but if the magma is beneath the earth's surface, these elements begin to seperate forming new magmas. Each of of these magmas has a different composition.

This residu magma causes hydrothermal solutions to slowly erode their way into nearby rocks by moving through small cracks etc, the minerals in this solution will cling to the sides of these cracks and form hydrothermal veins.

Sedimentary mineralization: Nature can leave elements on several places either with some help from the wind or the water, this sedimentation usually leaves things like gypsum and borate behind and with the help of some micro organisms new minerals are formed.

When hot magma penetrates surrounding rocks, these are damaged by the heat of the magma, especially when a rock comes in direct contact with it.. The minerals that form at the point/line of contact are.. yup.. contact minerals

The other type has to do with large bodies of rock that were formed on the surface of the earth but ended up way beneath it later, these rocks are subjected to very high pressure and temperatures and change into metamorphic minerals on a regional scale.

Relative Density: Is the relative number that defines how much times heavier or lighter a mineral is compared to an equal volume of water (at 4 degrees celsius)

Hardness: The ability to withstand mechanical damage, determined by it's ability to scratch another mineral or be scratched. Talc(1) is the bottom of this scale, Diamond(10) the top. This method is also refered to as the Moh scale.

Optical properties: Does the mineral have a constant colour? Is it translucent? Is it multi-coloured? Things like that, all thing you can or can't see. Most minerals don't have a constant colour, but if you rub it over a sheet of paper or another white surface that won't crumble but rip or break, it leaves some colouredpowder of the mineral behind.. the colour of this powder stripe is usually constant and is very important when identifying minerals

Magnetism: Is this mineral magnetic? If so, how strongly? or, Can this mineral be magnetised?

Ok, this is it.. There's nothing more I can say on the subject, I'm not a mineralogist and everything jotted down here is a compile of the things I've read on the subject in the past (and actually remembered or wrote down)..

There are about 2600 identified minerals right now, most of which have different varieties. Ow and one other thingy, I said that everything natural you can stick a note on with it's chemical formula is a mineral well, there's one exception I know of; Mercury aka Quicksilver.

A mineral is a naturally occuring, generally inorganic solid with a definite chemical composition that is fixed or varies within fixed limits, and a highly ordered internal atomic arrangement, which repeats itself in three dimensions.

Lets break this down:

Naturally occuring distinguishes between those things found in nature and those created in laboratories (synthetics) or by other man made means. This can be come confusing when minerals are formed in or on man made structures by natural processes, such as salt or calcium carbonate precipitating out of water in a gutter.

Inorganic means anything created by organism can not be considered a mineral. However, aragonite can be excreted by some organisms to create their shell, and this is often still considered a mineral. This might be because it is more convienient to say "this shell is made of the mineral aragonite" than it is to say "this shell is made of calcium carbonate with the crystalline structure of aragonite". This is a bit of a grey area, as many organic compounds are changed by inorganic processes, such that they may be unrecognizable as organic fragments or are reworked by temperature, pressure or time to create a new compounds or a change in the internal structure. Petroleum and coal are usually termed mineral fuels, ignoring their organic origin.

The solid part is fairly straight forward, excluding gases and liquids, which would be excluded by the ordered internal structure requirement as well. Water is not a mineral but ice can be if it has an ordered structure.

The chemical composition part is also fairly straight forward. For example,olivine is a mineral composed of the two end members forsterite, Mg2SiO4, and fayalite, Fe2SiO4. Thus olivine can be represented as a mixture of the two by writing its formula as (Mg, Fe)2SiO4. This varies within the fixed limits of being a mixture of the two end members. A solid compound with a composition that is variable and cannot be expressed by a chemical formula would not be considered a mineral.

A highly ordered internal structure describes a structure of atoms or ions that repeats in a 3-D geometric pattern. This is the definition of a crystalline solid, so often times crystalline replaces this part of the defintion of a mineral. Any solid lacking this internal structure is called amorphous. An example of this would be the volcanic glass obsidian. Although it may have the same chemical composition as quartz, it is not a mineral because it cooled very quickly, "freezing" in the lack of structure characteristic of liquids. Other phenomena cause a lack of structure, such as damage by radiation. This often appears as a halo around the radioactive mineral in the rock, although it can ususally only be seen in thin section. Many mineral-like compounds lacking structure are termed mineraloids. The repeatition of the interal structure of atoms in three dimensions creates the faces of a mineral.

Minerals generally have a set of physical characteristics, such as melting point, conductivity, malleability, etc, but these are often highly dependent on purity, so this is not part of the definition of a mineral in most mineralogy texts. Most minerals are not pure substances, and even if they were, things such as twinning and enantiomorphism cause changes to some physical characteristics. The physical characteristics that are fairly reliable in mineral identification are density, optical characteristics viewed with a petrographic microscope, hardness, crystal system, lustre, and cleavage.

The study of minerals is called mineralogy, and this often includes the study of synthesized rock forming compounds.

Reference: Klien, C., 2002, The 22nd Edition of the Manual of Mineral Science. John Wiley and Sons Inc., New York.

An inorganic species or substance occurring in nature, having a definite chemical composition and usually a distinct crystalline form. Rocks, except certain glassy igneous forms, are either simple minerals or aggregates of minerals.

2.

A mine.

[Obs.]

Shak.

3.

Anything which is neither animal nor vegetable, as in the most general classification of things into three kingdoms (animal, vegetable, and mineral).